CN118382594A

CN118382594A - Methanol from biomass gasification

Info

Publication number: CN118382594A
Application number: CN202280082058.8A
Authority: CN
Inventors: I·穆西奥尼科; P·莫雷奥
Original assignee: Casale SA
Current assignee: Casale SA
Priority date: 2021-12-14
Filing date: 2022-12-06
Publication date: 2024-07-23
Also published as: EP4448445A1; MX2024007172A; AU2022411935A1; AR127820A1; CA3240635A1; KR20240125929A; JP2024546495A; ZA202403508B; US20250042829A1; WO2023110526A1

Abstract

A process (100) for synthesizing methanol (1) comprising the following steps: subjecting biomass (2) to a gasification process (6) in the presence of water vapor (5) and an oxidant (48); subjecting the gasifier stream (7) thus obtained to a water-gas shift conversion (10) and purification (14) to produce a synthesis gas (15) having hydrogen, carbon monoxide and CO2; mixing the synthesis gas (15) with a second synthesis gas stream (31) to produce a third synthesis gas stream (16); feeding the third synthesis gas stream (16) to a methanol synthesis loop (19), wherein crude methanol (20) and a tail gas (35) retaining methane are produced; and subjecting the tail gas (35) to a reforming step (25) in the presence of an oxidant (49) to produce the second synthesis gas stream (31).

Description

Methanol from biomass gasification

Technical Field

The invention belongs to the field of methanol production. In particular, the invention relates to a process and apparatus for synthesizing methanol.

Background

The gasification process involves the partial oxidation of a carbonaceous feedstock in the presence of a sub-stoichiometric amount of an oxidant (e.g., oxygen or air). The product of gasification is a synthesis gas that contains carbon monoxide, hydrogen and small amounts of carbon dioxide, water and methane in addition to incompletely combusted or oxidized solid residues.

There is an increasing interest in the art to use synthesis gas obtained from biomass gasification to produce bio-methanol. Biomass gasification is a complex process that requires consideration of conflicting requirements, such as the necessity to avoid melting of unburned residues and the necessity to keep the methane and carbon dioxide content in the synthesis gas as low as possible.

The unburned residues must be prevented from melting to avoid transfer of impurities (e.g., sulfur and alkali) into the syngas. The impurities may cause problems with deactivation of the methanol synthesis catalyst and corrosion problems in the plant. In contrast, the formation of methane must be limited because the gaseous product does not participate in the synthesis of methanol.

Conventional biomass gasification processes are typically carried out in the presence of oxygen and water vapor at relatively low temperatures (e.g., below 1000 ℃) and at medium-high pressures (typically comprised between 30 and 100 bar).

Unfortunately, due to the operating conditions employed (i.e., low temperature and high pressure), the synthesis gas obtained in the process retains a relatively high concentration of methane, for example, about 10-12% mole on a dry basis.

The large amount of methane retained in the synthesis gas is a disadvantage because it reduces the productivity and efficiency of the plant because unconverted methane is not utilized in the process, but is typically purged from the synthesis loop and combusted as tail gas.

Another disadvantage of reducing the cost and energy efficiency of a bio-methanol process relates to the utilization and purification of the water stream produced during the process.

In particular, methanol is obtained from the synthesis loop as a crude stream comprising impurities (i.e. dissolved gases such as methane, higher alcohols, aldehydes, ketones and water) and must be purified downstream of the synthesis loop to obtain a high purity product. Purification is typically carried out in a distillation section wherein high purity methanol product is separated from an aqueous stream contaminated with residual methanol and a stream containing the above impurities.

The water stream cannot be discharged directly to the environment, but must be treated in a suitable unit (for example in a scrubber) to reduce its CH3OH content. Obviously, said purification step increases the operating costs of the process and involves waste of resources, since the aqueous stream thus obtained is then discharged from the plant.

Therefore, in view of the above considerations, there is a great need to develop an energy efficient, economically viable and resource efficient process and apparatus for synthesizing methanol.

US2014/0145819 discloses a mixing device for producing liquid fuel from a hydrogen and carbon monoxide containing stream resulting from steam reforming of gasified solid carbonaceous feedstock and light fossil fuel.

Disclosure of Invention

The object of the present invention is to solve the drawbacks of the prior art.

The present invention is based on the insight that in order to obtain a resource efficient and energy efficient bio-methanol process, all the resources (i.e. methane and water streams) generated during the synthesis are recycled in the process.

Accordingly, one aspect of the present invention is a process for the synthesis of methanol according to claim 1.

The process includes the step of feeding a synthesis gas effluent obtained from biomass gasification and from tail gas reforming to a methanol synthesis loop. In the methanol synthesis loop, catalytic conversion of carbon oxides to methanol is performed under methanol synthesis conditions to obtain a methanol product and a methane rich tail gas, wherein the tail gas is partially recycled to the reformer for further conversion to synthesis gas.

Another aspect of the invention is an apparatus for producing methanol according to the claims.

The apparatus includes a front end for producing a first synthesis gas stream from biomass gasification, a methanol synthesis loop for producing crude methanol and a methane-rich tail gas, and a tail gas treatment section including a reforming unit for converting methane retained in the tail gas into a second synthesis gas stream. The first synthesis gas stream obtained from the gasification and the second synthesis gas stream obtained from the reforming, when mixed, form a third synthesis gas stream which is fed to the methanol synthesis loop.

The present invention provides an energy efficient and economically viable option for producing methanol because methane synthesized as an unwanted product during gasification can now be converted in the reformer into a useful stream, i.e. the second synthesis gas stream. The second synthesis gas stream thus obtained can then be converted into methanol to increase the productivity of the plant.

Another advantage is that an efficient reuse of the water stream produced in the plant can be achieved and that no methanol purification treatment of the water stream is required. A further advantage is that there is no water loss in the device, since the inlet and outlet of water are balanced, i.e. all the water produced in the process is recycled.

Detailed Description

The term biomass in the present invention includes, but is not limited to, wood materials (bark, wood chips, crushed aggregates and sawdust), pulp and paper industry residues, agricultural residues, organic municipal materials, sewage, manure and food processing byproducts.

In the process of the present invention, the biomass feedstock is fed to a gasification step in the presence of steam and an oxidant to produce a gasifier stream. The gasifier stream is then subjected to a water-gas shift conversion and to a purification step to produce a first synthesis gas stream that retains hydrogen and carbon monoxide.

The resulting first syngas stream is then mixed with the second syngas stream to produce a third syngas stream. The second synthesis gas stream is obtained by subjecting the tail gas extracted from the methanol synthesis loop to a reforming process.

The third synthesis gas stream is then sent to a methanol synthesis loop where a catalytic reaction is carried out to form crude methanol. In the methanol loop, catalytic conversion of carbon oxides to methanol is performed under methanol synthesis conditions to produce crude methanol and a tail gas that retains methane.

The tail gas extracted from the methanol synthesis loop is fed to a reforming step in the presence of an oxidant to produce the second synthesis gas stream, which is then mixed with the first synthesis gas stream obtained from the gasification unit.

According to a preferred embodiment, a series of pre-treatments are performed before feeding the biomass to the gasifier step to increase the gasification efficiency. Pretreatment may include drying, pyrolysis, and/or oven drying.

The gasification is performed in the presence of steam to increase the hydrogen content in the synthesis gas and in the presence of an oxidant, preferably oxygen. Oxygen may be produced on site by an air separation unit or a water electrolyzer. Preferably, the oxygen stream has a purity of more than 99% mole or preferably more than 99.5% mole.

After gasification, the synthesis gas obtained may have the following composition: the hydrogen content H2 is comprised between 55 and 65% by moles, preferably equal to or about 61.1% by moles; the nitrogen content N2 is comprised between 0.2 and 0.5% moles, preferably equal to or about 0.4% moles; the carbon monoxide CO content is comprised between 22 and 28% mole, preferably equal to or about 25.6% mole; the carbon dioxide CO2 content is comprised between 2 and 4% mole, preferably equal to or about 3.4% mole; the methane CH4 content is comprised between 8 and 10% mole, preferably equal to or about 9.5% mole; the Ar content is comprised between 0.02 and 0.05 mole%, preferably equal to or about 0.04 mole%.

Methanol synthesis catalysts are generally sensitive to tar, particulates, sulfur, excess CO2, and other impurities (e.g., sulfur). Thus, a gas cleaning stage may be provided after the gasification step.

According to a particularly preferred embodiment, the gasifier stream exiting the gasification stage may be subjected to a water gas shift conversion to adjust the H2/CO ratio.

The gas leaving the water gas shift conversion may be subjected to a cooling step before being sent to the CO2 removal step. CO2 removal may be performed by known processes and techniques, namely polyethylene glycol dimethyl ether (selexol), low temperature methanol wash (rectisol), MEA or MDEA chemisorption.

According to the invention, the off-gas leaving the methanol synthesis section is subjected to a reforming step, preferably under autothermal reforming conditions or under partial oxidation conditions in the presence of an oxidant. Preferably, the reforming step is carried out at a temperature of 1000 to 1500 ℃ or 1000 to 1300 ℃.

Preferably, the concentration of inert gas in the synthesis loop is less than 40% mol.

According to a particularly preferred embodiment, the step of reforming the off-gas comprises a pretreatment of the off-gas prior to the reforming reaction. It is particularly preferred that the tail gas extracted from the methanol synthesis loop is subjected to a saturation step with water to obtain a saturated stream prior to the reforming process. More preferably, the saturated stream is further contacted with steam to obtain a conditioned stream, and the conditioned stream is sent to the reforming step. Preferably, the conditioned stream is characterized by a steam to carbon ratio S/C comprised between 1.0 and 2.0.

According to another particularly preferred embodiment, the crude methanol is subjected to a purification step to produce a methanol product, a first fusel oil stream, a second light hydrocarbon stream, and a recovered water stream.

Preferably, the recovered aqueous stream is supplied to the saturation step. Advantageously, all contaminated water produced in the plant is recycled in the process and no additional water treatment is required to purify the water. In addition, efficient utilization of resources is achieved.

Preferably, said conditioned stream obtained after mixing the saturated aqueous stream with water vapor is further treated in a preheating stage to obtain a temperature-conditioned stream having a temperature comprised in the range 600 ℃ to 750 ℃, or preferably equal to 650 ℃ or about 650 ℃.

According to an embodiment of the invention, the further product of the methanol synthesis loop is a gaseous mixture of flash gas and tail gas, and the preheating stage is carried out under direct combustion conditions and is combusted from the gaseous mixture of the first fusel oil stream, the second light hydrocarbon stream and the flash gas and tail gas.

The term fusel oil is used hereinafter to refer to a mixture of heavier compounds including water, higher alcohols, methanol, and alkanes. Conversely, the term light hydrocarbon is used to denote a gaseous product that is lighter than methanol.

According to another embodiment of the invention, the preheating stage is carried out in a conventional heat exchanger or in an electric heater and the temperature regulated stream is mixed with the first fusel oil stream recovered from the purification step before being sent to the reforming step.

According to a particularly interesting application of the invention, the second synthesis gas stream obtained from the reforming process is subjected, in sequence, to a cooling step with the recovered aqueous stream produced in the purification step, and to a separation step to condense out condensed water, before being mixed with the first synthesis gas stream.

Preferably, said condensed water is mixed with said recovered water stream from the purification step prior to exchanging heat with said second synthesis gas stream in said cooling step.

According to an embodiment, the cooling step comprises a steam generation step, wherein a gas mixture of the second light hydrocarbon stream obtained from the purification section and the flash gas and tail gas obtained from the methanol synthesis loop is combusted in the steam generation step to generate superheated steam. Preferably, the combustion conditions in the steam generating step are established by a fired heater.

Or superheated steam may be generated in the steam generating step by combusting the first fusel oil stream, the second light hydrocarbon stream, and a gaseous mixture of the flash gas and tail gas.

Some embodiments of the invention relate to the use of various purge streams for methanol synthesis processes. Typically, a purge gas is withdrawn from the methanol synthesis loop to avoid accumulation of inert gases, and the purge gas is sent to a Hydrogen Recovery Unit (HRU) to recover the hydrogen contained therein, possibly after washing with water, to produce a recovered hydrogen stream and a tail gas, referred to as HRU tail gas. The HRU tail gas may contain residual hydrogen and methane. Other purge streams from the methanol process may include: flash gas from one or more separators, light ends from crude methanol distillation, and fusel oil. In certain embodiments, at least a portion of the HRU tail gas is recycled to the reforming section as process gas. Other purge streams and optionally the remainder of the HRU tail gas may be recycled as fuel to the fired heater.

In interesting embodiments of the invention, the HRU tail gas provides most of the process feed to the reforming step, or more preferably all of the process feed to the reforming step. In the latter case, an important advantage of the present invention is that no additional fossil fuel is required for the reforming step. The reforming step is said to be carried out in series with respect to the gasification step.

For example, according to embodiments of the present invention, since the process feed to the autothermal reformer is provided entirely by the tail gas removed from the methanol synthesis process fed to the gasifier, the autothermal reformer and the gasifier may be considered to operate in series.

Preferably, the HRU tail gas provides at least 80% or at least 90% or even more preferably 100% of the process feed to the reforming step.

It is particularly preferred that the reforming step is carried out in an autothermal reformer, the process feed of which is provided entirely by methanol off-gas. In an alternative embodiment, the reforming step is performed in a partial oxidation reactor.

The HRU tail gas may be fed to the reforming step after appropriate treatment. The treatment preferably includes saturation with water, and may further include preheating.

According to another interesting feature of the invention, the reforming step comprises preheating the process stream to be reformed in a fired heater, and the fuel of said fired heater is at least partially provided by one or more of the above-mentioned purge streams, possibly with a small fraction of HRU tail gas.

It is particularly preferred to fuel the fired heater with the purge stream and additionally with a portion of the make-up gas of the methanol synthesis loop, which make-up gas is used as a trim fuel to reliably control combustion. For safety reasons, it is more preferred to use a natural gas stream to supply the ignition burner of the combustion heater.

In a preferred embodiment, the reforming step is carried out in an autothermal reformer and the process feed at the inlet of said autothermal reformer comprises at least 20 mole% methane on a dry basis, preferably equal to or about 50 mole% methane on a dry basis.

In embodiments based on autothermal reforming, the reforming section preferably includes an autothermal reformer as the sole catalytic reactor in the reforming section.

According to the invention, the apparatus comprises a front end comprising a gasification stage configured to convert a biomass feedstock into a gasifier stream in the presence of steam and an oxidant to produce a first synthesis gas stream retaining hydrogen, carbon monoxide and residual CO2, a water gas shift converter, and a CO2 removal stage.

The device also comprises a methanol synthesis loop, a tail gas treatment section and a pipeline provided with a compression unit, wherein the compression unit is connected with the front end of the methanol and the methanol synthesis loop.

The methanol synthesis loop includes a methanol synthesis reactor configured to produce crude methanol and tail gas.

The tail gas treatment section connects a methanol synthesis loop with the pipeline connecting the front end of the methanol and the methanol synthesis loop.

The tail gas treatment section comprises a water saturation column in communication with the methanol synthesis loop and configured to generate a saturated water stream; a preheating unit in communication with the saturation column; and a reforming unit in fluid communication with the preheating unit and configured to generate a second syngas stream.

The apparatus further includes a line connecting the reforming unit and the compression unit.

The apparatus may further comprise a line configured to supply water vapor to the saturated water stream prior to the preheating unit, and a purification section in communication with the methanol synthesis loop.

Preferably, the purification section is a multi-column distillation section and is configured to produce a methanol product, a recovered water stream, a first fusel oil stream, and a second light hydrocarbon stream.

According to an embodiment, the apparatus further comprises a line connecting the preheating unit and the purification section, and the preheating unit is a fired heater and the reforming unit is an autothermal reformer.

Or the apparatus further comprises a line connecting the purification section and the reforming unit, and the reforming unit is a partial oxidation reactor.

Preferably, when the reforming unit is a partial oxidation reactor, the preheating unit is a conventional heat exchanger or an electric heater, and conversely, when the reforming unit is an autothermal reformer, the preheating unit is an electric heater or a combustion heater.

According to various embodiments, when the preheating unit is a fired heater, the latter may be combusted with the first fusel oil stream, the second light hydrocarbon stream, and the gas mixture of flash gas and tail gas.

The apparatus preferably comprises a cooling section comprising a steam generating section provided with a combustion heater arranged downstream of the reforming unit and in fluid communication with the methanol synthesis loop and with the purification section.

The methanol synthesis loop preferably comprises a methanol reactor provided with a fixed bed operating in a pressure range of 50 to 120 bar and in a temperature range of 200 to 300 ℃.

Drawings

Fig. 1 shows a schematic process arrangement of a methanol plant according to a preferred embodiment of the invention.

Fig. 2 shows a schematic process arrangement of a methanol plant according to an alternative embodiment of the invention.

Fig. 3 shows a schematic process arrangement of a methanol plant according to another embodiment of the invention.

Description of The Preferred Embodiment

Fig. 1 shows a methanol plant 100 for synthesizing methanol 1 comprising a front end 101, a methanol synthesis loop 19, a purification section 21 and a tail gas treatment section 102.

The front end 101 of the methanol comprises a pretreatment section 3, a gasifier 6, a gas cleaning unit 8, a water gas shift reactor 10 and a carbon dioxide CO ₂ removal unit 14.

The tail gas treatment section 102 includes a water saturation column 36, a preheating unit, and a reforming unit in communication with the methanol synthesis loop 19. In the embodiment of fig. 1, the preheating unit comprises a combustion heater 23 and the reforming unit comprises an autothermal reformer 25. The gas treatment section 102 also includes a cooling section 50 and a condenser 30.

An air separation unit 47 provides oxygen-containing streams 48, 49 to the gasifier 6 and to the autothermal reformer 25.

The methanol synthesis loop 19 and the purification section 21 are provided with a methanol synthesis reactor and a distillation unit (not shown), respectively. The methanol synthesis loop 19 and the purification section 21 are in communication with each other via a line 51 carrying a crude methanol stream 20.

The methanol synthesis process will now be described with reference to fig. 1. The biomass feedstock 2 is fed to a pretreatment stage 3 where the moisture of the feedstock 2 is reduced to a suitable level to produce a dried biomass 4.

The dried biomass 4 is fed into a gasifier 6 in the presence of water vapor 5 and oxygen 48 to produce a gasifier stream 7. The gasifier stream 7 is then sent to a gas cleaning unit 8 where impurities (e.g., sulfur and alkali) are removed in the gas cleaning unit 8 to produce a purified gas 9; the purified gas 9 is then fed to a water gas shift reactor 10, wherein the S/C ratio of the purified gas 9 is adjusted to a value suitable for methanol synthesis to produce an adjusted make-up gas 13.

The conditioned make-up gas 13 is then treated in a CO2 removal unit 14. The product of the CO2 removal unit 14 is a first syngas stream 15 that is mixed with a second syngas stream 31 extracted from a condenser 30 to produce a third syngas stream 16. The third synthesis gas stream 16 is suitable for conversion in a methanol synthesis loop to form a methanol make-up gas.

The methanol make-up gas 16 is fed to the suction section of a compressor 17 to produce a compressed make-up gas 18, which compressed make-up gas 18 is then fed to a methanol synthesis loop 19.

In the methanol synthesis loop 19, crude methanol 20 is synthesized under methanol synthesis conditions. Other effluents of the methanol synthesis loop 19 are off gas 35 and a gaseous mixture 34 of flash and off gas. Both the tail gas 35 and the gas mixture 34 are methane-retaining gas streams. The off-gases 34 and 35 in the lines may be taken from a hydrogen recovery unit that processes the purge gas removed from the methanol synthesis loop.

The crude methanol 20 is then passed to a purification/distillation section 21 to produce a pure methanol product 1, a recovered water stream 33, a first fusel oil stream 40, and a second light hydrocarbon stream 41.

The tail gas 35 is supplied to a saturation column 36 where the saturation column 36 is saturated with hot water 43 to produce a saturated stream 37.

The saturated stream 37 is then contacted with steam 38 to produce a conditioned stream 39, which conditioned stream 39 is preheated in the fired heater 23 and fed to the autothermal reformer 25 after preheating. The stream 39 represents the entire feed to the autothermal reformer 25.

The fired heater 23 is fired with the flash gas and tail gas mixture 34, the first fusel oil stream 40, and the second light hydrocarbon stream 41. The effluent of the fired heater 23 is a temperature regulated stream 24 which is then sent to an autothermal reformer 25.

The product of the autothermal reformer 25 is a reformed gas 26, which reformed gas 26 is fed in turn to a cooling section 50 and a condenser 30 to produce condensed water 32 and said second synthesis gas stream 31.

As described above, the second syngas stream 31 is then mixed with the first syngas stream 15 from the CO2 removal unit 14.

The cooling section 50 includes a steam generating section 27 and one or more heat exchangers 28. The recovered water stream 33 from the purification section 21 is supplied to a heat exchanger 28 to exchange heat with the cooled gas effluent 53 of the steam generation section 27. The heat exchanger 28 produces a hot water stream 43 that is delivered to the saturation column 36; the cooled gas stream 29 effluent from heat exchanger 28 is fed to condensing section 30.

As is evident from the above examples, all the resources generated in the process, namely the tail gas 35 and the recovered water stream 33, are recycled inside the process. In order to avoid the accumulation of impurities present in the water from distillation, a purge stream may be discharged at the bottom of the saturation column.

Advantageously, due to the above configuration, applicants have found that the productivity of methanol can be increased by about 30% compared to conventional bio-methanol processes, wherein the tail gas 35 and the recovered water stream 33 are not recycled in conventional bio-methanol processes.

Furthermore, the carbon efficiency, calculated as moles of pure CH3OH in crude CH3 OH/moles of (co+co2+ch4) in make-up gas, increased from 72% to 93%.

Fig. 2 shows a methanol plant 100 according to an alternative embodiment of the invention. This embodiment differs from that of fig. 1 in that it uses a partial oxidation reactor (POX reactor) 125.

The first synthesis gas stream 15 is synthesized according to the previous steps. Here, the first synthesis gas stream 15 is mixed with the second synthesis gas stream 31 and compressed in a compressor 17 to produce a compressed gas 18, which compressed gas 18 is then fed to a methanol synthesis loop 19.

The effluent from the methanol synthesis loop is a gaseous mixture 34 of flash and off-gas, a crude methanol stream 20 and off-gas 35. The crude methanol stream 20 is fed to a purification section 21 to produce a methanol product 1, a recovered water stream 33, a first fusel oil stream 40, and a second light hydrocarbon stream 41.

As in the previously described embodiment, the tail gas is supplied to a saturation column 36 to produce a saturated gas 37, and then the saturated gas 37 is mixed with steam 38 to produce a conditioned stream 39.

The conditioned stream 39 is then passed to a preheating unit 23, in this embodiment the preheating unit 23 is represented by a conventional heat exchanger or electric heater, to ultimately produce a temperature conditioned stream 24.

The temperature conditioned stream 24 is then mixed with the first fusel oil stream 40 to produce a gaseous product 55, which gaseous product 55 is in turn fed to the partial oxidation reactor 125.

The product of the partial oxidation is the reformed gas 26, which is then treated in a cooling step 50. The cooling step includes a steam generating section 27 and a heat exchanger 28. The steam generating section comprises a fired heater (not shown in the figures) which is fired with a fuel gas 44, which fuel gas 44 is obtained by mixing said second light hydrocarbon stream 41 with said gas mixture 34 of flash gas and tail gas.

As in the previously described embodiment, the recovered water stream 33 effluent from the purification section 21 is supplied to the heat exchanger 28 to indirectly exchange heat with the gas effluent 53 of the steam generation section 27.

The effluent from heat exchanger 28 is a hot water stream 43 and a cooling stream 29. The hot water stream 43 is sent to the saturation column 36 while the cooling stream 29 is sent to the syngas cleaning and condensing section 30.

The effluent of the condensing section 30 is condensed water 32 and the second synthesis gas stream 31. The condensed water 32 is mixed with the recovered water stream 33 and then passed through a heat exchanger 28 to produce hot water 43, which hot water 43 is then supplied to a saturation tower 36.

Fig. 3 shows an embodiment in which the steam generation section 27 includes a fired heater that combusts with a gas mixture 34 of flash gas and tail gas and a first fusel oil stream 40 and a second light hydrocarbon stream 41.

In a further embodiment of the invention, the preheating unit 23 supplied with the conditioned stream 39 may be an electric heater.

Claims

1. A process (100) for synthesizing methanol (1), comprising the steps of:

a) Subjecting a biomass feedstock (2) to a gasification process (6) in the presence of steam (5) and an oxidant (48) to produce a gasifier stream (7);

b) Subjecting the gasifier stream (7) to a water gas shift conversion (10) and a purification step (14) to produce a first synthesis gas stream (15) retaining hydrogen, carbon monoxide and CO 2;

c) Mixing the first (15) and second (31) syngas streams to produce a third syngas stream (16);

d) Feeding the third synthesis gas stream (16) to a methanol synthesis loop (19), wherein catalytic conversion of carbon oxides to methanol is performed under methanol synthesis conditions, obtaining crude methanol (20) and a tail gas (35) retaining methane;

e) -subjecting said tail gas (35) to a reforming step (25) in the presence of an oxidant (49) to generate said second synthesis gas stream (31) of step c).

2. The process according to claim 1, wherein the reforming step (25) at point e) is performed under autothermal reforming conditions or under partial oxidation conditions.

3. Process according to claim 1 or 2, wherein at least one of the oxidizing agent (48) of step a) and the oxidizing agent (49) of step e) is an oxygen stream having a purity higher than 99% molar or preferably higher than 99.5% molar.

4. A process according to any preceding claim, wherein step e) comprises subjecting the tail gas (35) obtained in step d) to a saturation step (36) with water (43) to obtain a saturated stream (37), and further contacting the saturated stream (37) with water vapor (38) to obtain a conditioned stream (39), and subjecting the conditioned stream (39) to the reforming step (25).

5. A process according to claim 4, wherein the conditioned stream (39) has a water vapour to carbon ratio S/C comprised between 1.0 and 2.0.

6. A process according to any preceding claim, wherein the crude methanol (20) is further subjected to a purification step (21) to produce a methanol product (1), a first fusel oil stream (40), a second light hydrocarbon stream (41) and a recovered water stream (33).

7. A process according to claim 6, wherein the recovered aqueous stream (33) is supplied to the saturation step (36).

8. A process according to any one of claims 4 to 7, wherein the conditioned stream (39) is preheated in a preheating stage (23) before being fed to the reforming step (25) to obtain a temperature-conditioned stream (24) comprising a temperature in the range 600 to 750 ℃, or preferably equal to or about 650 ℃.

9. Process according to any one of the preceding claims, wherein the other product of the methanol synthesis loop (19) is a gaseous mixture of flash and tail gas (34), and the preheating stage (23) is carried out under direct combustion conditions and is combusted by the first fusel oil stream (40), the second light hydrocarbon stream (41) and the gaseous mixture of flash and tail gas (34).

10. Process according to claim 8, wherein the temperature-regulated stream (24) is mixed with the first fusel oil stream (40) recovered from the purification step (21) before being sent to the reforming step (25).

11. A process according to any preceding claim, wherein the second synthesis gas stream (31) of step c) is subjected to a cooling step (50) with the recovered water stream (33) produced in the purification step (21) and to a separation step (30) to condense out condensed water (32) before being mixed with the first synthesis gas stream (15).

12. A process according to claim 11, wherein the condensed water (32) is mixed with the recovered water stream (33) from the purification step (21) before exchanging heat with the second synthesis gas stream (31) in the cooling step (50).

13. Process according to claim 11 or 12, wherein the cooling step (50) comprises a steam generation step (27), wherein in the steam generation step (27) a gas mixture (34) of the flash gas and tail gas, the second light hydrocarbon stream (41) and optionally the first fusel oil stream (40) are combusted to generate superheated steam.

14. A process according to any one of the preceding claims, wherein the tail gas (35) provides most or all of the process feed to the reforming step (e).

15. The process of any one of the preceding claims, wherein the reforming step comprises preheating the process stream to be reformed in a fired heater and the fuel of the fired heater comprises one or more purge streams obtained from the synthesis of crude methanol and/or purge streams obtained from the purification of crude methanol and the fuel of the fired heater may comprise one or more of the following: a portion of the tail gas (35); a portion of the third synthesis gas stream (16) of step d); a natural gas stream.

16. The process according to any of the preceding claims, wherein the reforming step (e) is performed in an autothermal reformer (25) and the process feed at the inlet of the autothermal reformer comprises at least 20 mol% methane on a dry basis, preferably equal to or about 50 mol% methane on a dry basis.

17. An apparatus for producing methanol (1), comprising:

a) A front end (101) comprising a gasification stage (6), a water gas shift converter (10) and a CO2 removal stage (14), the gasification stage (6) configured for converting a biomass feedstock (2) to a gasifier stream (7) in the presence of water vapor (5) and an oxidant (48) to produce a first synthesis gas stream (15) retaining hydrogen, carbon monoxide and CO 2;

b) A methanol synthesis loop (19) comprising a methanol synthesis reactor configured to generate crude methanol (20) and a tail gas (35);

c) A pipeline provided with a compression unit (17) which is connected with the front end (101) of the methanol and the methanol synthesis loop (19);

d) -a tail gas treatment section (102) connecting the methanol synthesis loop (19) with the line connecting the front end of methanol (101) and the methanol synthesis loop (19), wherein the tail gas treatment section (102) comprises:

-a Shui Baohe column (36) arranged downstream of the methanol synthesis loop (19) and configured to generate a saturated stream (37);

-a preheating unit (23) in communication with the saturation column (36);

-a reforming unit (25) in communication with the preheating unit (23) and configured to generate a second synthesis gas stream (31);

-a line connecting the reforming unit (25) and the compression unit (17).

18. The apparatus of claim 17, further comprising:

-a line configured to supply water vapor (38) to the saturated stream (37) before the preheating unit (23);

A purification section (21) in communication with the methanol synthesis loop (19), preferably the purification section (21) is a multi-column distillation section and is configured to produce a methanol product (1), a recovered water stream (33), and a first fusel oil stream (40) and a second light hydrocarbon stream (41).

19. The apparatus of claim 18, further comprising:

A pipeline connecting the preheating unit (23) and the purification section (21), and the preheating unit (23) is a combustion heater and the reforming unit (25) is an autothermal reformer,

Or (b)

-A line connecting the purification section (21) and the reforming unit (25), and the reforming unit is a partial oxidation reactor.

20. The plant according to claim 18 or 19, further comprising a cooling section (50) comprising a steam generating section (27) provided with a combustion heater arranged downstream of the reforming unit (25) and in fluid communication with the methanol synthesis loop (19) and the purification section (21).